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package com.hardcode.gdbms.engine;

import java.io.IOException;

import com.hardcode.gdbms.engine.data.DataSource;

import com.hardcode.gdbms.engine.data.DriverException;

import com.hardcode.gdbms.engine.data.ReadDriver;

import com.hardcode.gdbms.engine.data.indexes.IndexFactory;

import com.hardcode.gdbms.engine.data.indexes.VariableIndexSet;

import com.hardcode.gdbms.engine.instruction.Expression;

import com.hardcode.gdbms.engine.instruction.FieldNotFoundException;

import com.hardcode.gdbms.engine.instruction.IncompatibleTypesException;

import com.hardcode.gdbms.engine.instruction.SemanticException;

import com.hardcode.gdbms.engine.values.BooleanValue;

import com.hardcode.gdbms.engine.values.Value;

/**

 * Representa una fuente de datos que contiene una cl?usula where mediante la

 * cual se filtran los campos

 *

 * @author Fernando Gonz?lez Cort?s

 */

public class FilteredDataSource implements DataSource {

    private DataSource source;

    private Expression whereExpression;

    private VariableIndexSet indexes;

    /**

     * Creates a new FilteredDataSource object.

     *

     * @param source DataSource que se va a filtrar

     * @param whereExpression Expresi?n de la cl?usula where

     */

    public FilteredDataSource(DataSource source,

        Expression whereExpression) {

        this.source = source;

        this.whereExpression = whereExpression;

    }

    /**

     * M?todo que construye el array de ?ndices de las posiciones que las filas

     * filtradas ocupan en el DataSource origen

     *

     * @throws DriverException Si se produce un fallo en el driver al acceder a

     *         los datos

     * @throws IOException Si se produce un error accediendo al DataSource

     *         subyacente

     * @throws SemanticException Si se produce alg?n error sem?ntico al evaluar

     *         la expresi?n

     * @throws IncompatibleTypesException Si la expresi?n where no evalua a

     *         booleano

     */

    public void filtrar()

        throws DriverException, IOException, SemanticException {

        indexes = IndexFactory.createVariableIndex();

        indexes.open();

        for (long i = 0; i < source.getRowCount(); i++) {

            try {

                if (((BooleanValue) whereExpression.evaluateExpression(i)).getValue()) {

                    indexes.addIndex(i);

                }

            } catch (ClassCastException e) {

                throw new IncompatibleTypesException(

                    "where expression is not boolean");

            }

        }

        indexes.indexSetComplete();

    }

    /**

     * @see com.hardcode.gdbms.engine.data.DataSource#open()

     */

    public void start() throws DriverException {

        source.start();

    }

    /**

     * @see com.hardcode.gdbms.engine.data.DataSource#close()

     */

    public void stop() throws DriverException {

        source.stop();

        try {

            indexes.close();

        } catch (IOException e) {

            throw new DriverException(e);

        }

    }

    /**

     * @see com.hardcode.gdbms.engine.data.DataSource#getName()

     */

    public String getName() {

        return source.getName();

    }

    /**

     * @see com.hardcode.gdbms.engine.data.FieldNameAccess#getFieldIndexByName(java.lang.String)

     */

    public int getFieldIndexByName(String fieldName)

        throws DriverException, FieldNotFoundException {

        return source.getFieldIndexByName(fieldName);

    }

    /**

     * @see com.hardcode.gdbms.engine.data.ReadAccess#getFieldValue(long, int)

     */

    public Value getFieldValue(long rowIndex, int fieldId)

        throws DriverException {

        try {

            return source.getFieldValue(indexes.getIndex(rowIndex), fieldId);

        } catch (IOException e) {

            throw new DriverException(e);

        }

    }

    /**

     * @see com.hardcode.gdbms.engine.data.ReadAccess#getFieldCount()

     */

    public int getFieldCount() throws DriverException {

        return source.getFieldCount();

    }

    /**

     * @see com.hardcode.gdbms.engine.data.ReadAccess#getFieldName(int)

     */

    public String getFieldName(int fieldId) throws DriverException {

        return source.getFieldName(fieldId);

    }

    /**

     * @see com.hardcode.gdbms.engine.data.ReadAccess#getRowCount()

     */

    public long getRowCount() throws DriverException {

        return indexes.getIndexCount();

    }

        /**

         * @see com.hardcode.gdbms.engine.data.DataSource#getDBMS()

         */

        public String getDBMS() {

                return source.getDBMS();

        }

        /**

         * @see com.hardcode.gdbms.engine.data.DataSource#getDriver()

         */

        public ReadDriver getDriver() {

                return null;

        }

}